The present invention relates to an antimicrobial composition. More particularly, the present invention relates to an antimicrobial composition which comprises an isothiazolone compound, suppresses decomposition of the isothiazolone compound and reduces irritation of skin caused by the isothiazolone compound.
Isothiazolone compounds such as 5-chloro-2-methyl-4-isothiazoline-3-one as a typical example exhibit an excellent antimicrobial property and are widely used as slime control agents, bactericides, algaecides and fungicides in various systems such as cooling water systems, paper and pulp industry, coating materials industry, adhesive materials industry, treatments of cutting oils and sewage treatments. However, isothiazolone compounds are very unstable and stability of agents containing these compounds must be improved in order to use the agents effectively. Therefore, various studies have been conducted on the improvement.
For example, in the specification of Japanese Patent Application Publication Showa 54(1979)-23968, complexes of isothiazolone compounds with metal salts such as calcium chloride and zinc chloride are proposed as a complex which have the activity for killing organisms, are useful for controlling various types of organisms, particularly microorganisms, and not easily decomposed in the presence of ordinary additives or contaminating substances or in severe conditions and show excellent heat stability. In the specification of the U.S. Pat. No. 3,870,795, it is reported that isothiazolone compounds can be stabilized by suppressing decomposition by addition of metal nitrates such as calcium nitrate and magnesium nitrate or metal nitrites such as sodium nitrite and calcium nitrite to solutions of isothiazolone compounds.
In the specifications of Japanese Patent Application Laid-Open Nos. Showa 61(1986)-56174 and Showa 61(1986)-212576, stabilized solutions of isothiazolone compounds prepared by addition of metal salts such as copper chloride, sodium chloride, magnesium chloride and copper nitrate to solutions of isothiazolone compounds such as 5-chloro-2-methyl-4-isothiazoline-3-one in propylene glycol, 1,5-pentanediol or benzyl alcohol, are proposed.
However, the above agents and solutions had drawbacks in that stability of the isothiazolone compounds markedly deteriorates when the agents and solutions are further diluted with water or organic solvents. In the specification of Japanese Patent Application Laid-Open No. Heisei 5(1993)-124917, a method for protecting isothiazolone compounds from decomposition using compounds containing sulfur such as L-cystine in combination with isothiazolone compounds is proposed. However, this method has a drawback in that L-cystine has a small solubility in water and hydrophilic organic solvents and it is difficult to mix L-cystine with isothiazolone compounds. Therefore, an antimicrobial compound which suppresses decomposition of isothiazolone compounds and shows excellent stability has been desired. Isothiazolone compounds often irritate skin and agents containing isothiazolone compounds must be handled with sufficient care. In the specification of Japanese Patent Application Laid-Open No. Heisei 5(1993)-246807, compositions containing polycation compounds such as polylysine and isothiazolone compounds are disclosed. However, it is known that these compositions do not show the effect of suppressing decomposition of the isothiazolone compounds.
An object of the present invention is to provide an antimicrobial composition which comprises an isothiazolone compound, suppresses decomposition of the isothiazolone compound and reduces irritation of skin caused by the isothiazolone compound.
As the result of extensive studies to achieve the above object, it was found that specific aminocarboxylic acids and derivatives thereof exhibit the effect of stabilizing isothiazolone compounds and reducing irritation of skin caused by isothiazolone compounds. The present invention has been completed on the basis this knowledge.
The present invention provides:
(1) An antimicrobial composition comprising an isothiazolone compound represented by general formula [1] or general formula [2] and an aminocarboxylic acid represented by general formula [3] or a derivative of the aminocarboxylic acid: 
wherein R1 represents hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group or an aralkyl group, X and Y each represents hydrogen atom or a halogen atom or form a benzene ring in combination with carbon atoms at 4- and 5-positions of the isothiazolone compound, M represents a cation of an alkali metal, an alkaline earth metal, a heavy metal or an amine, Z represents an anion forming, in combination with the cation represented by M, a compound having a sufficient solubility to form a complex compound, a represents 1 or 2 and n represents an integer required for the anion represented by Z to satisfy a valence of the cation represented by M; 
wherein R2 represents hydrogen atom or an alkyl group having 1 to 5 carbon atoms unsubstituted or substituted with carboxyl group, R3 represents a linear or branched alkylene group having 1 to 5 carbon atoms, R4 represents hydrogen atom or an alkyl group having 1 to 5 carbon atoms unsubstituted or substituted with carboxyl group, carbamoyl group, hydroxyl group, phenyl group, hydroxyphenyl group, ureido group, methylthio group or 4-imidazolyl group, R2 and R4 form a heterocyclic group unsubstituted or substituted with hydroxyl group or oxo group in combination with Nxe2x80x94(R3)bxe2x80x94C and b represents 0 or 1; and
(2) An antimicrobial composition according to (1), wherein the derivative of the aminocarboxylic acid represented by general formula [3] is a metal salt of the aminocarboxylic acid represented by general formula [3]; a compound having a structure in which the aminocarboxylic acids represented by general formula [3] of one or more types are bonded to each other through a peptide bond or a metal salt of the compound; a compound having a structure in which the aminocarboxylic acid represented by general formula [3] is bonded to a different aminocarboxylic acid through a peptide bond or a metal salt of the compound; an N-acetyl compound of the aminocarboxylic acid represented by general formula [3] or a metal salt of the compound; or an amide of the aminocarboxylic acid represented by general formula [3].
Preferable embodiments of the present invention include:
(3) An antimicrobial composition described in any of (1) and (2), which comprises 0.1 to 10% by weight of the isothiazolone compound represented by general formula [1] or general formula [2]; and
(4) An antimicrobial composition described in any of (1), (2) and (3), which comprises the aminocarboxylic acid or the derivative thereof represented by general formula [3] in an amount by mol 0.1 to 50 times the amount by mol of the isothiazolone compound represented by general formula [1] or general formula [2].
The antimicrobial composition of the present invention comprises an isothiazolone compound represented by general formula [1] or general formula [2] and an aminocarboxylic acid represented by general formula [3] or a derivative of the aminocarboxylic acid. 
In general formula [1] and general formula [2], R1 represents hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group or an aralkyl group, X and Y each represents hydrogen atom or a halogen atom or form a benzene ring in combination with carbon atoms at 4- and 5-positions of the isothiazolone compound, M represents a cation of an alkali metal, an alkaline earth metal, a heavy metal or an amine, Z represents an anion forming, in combination with the cation represented by M, a compound having a sufficient solubility to form a complex compound, a represents 1 or 2 and n represents an integer required for the anion represented by Z to satisfy a valence of the cation represented by M. 
In general formula [3], R2 represents hydrogen atom or an alkyl group having 1 to 5 carbon atoms unsubstituted or substituted with carboxyl group, R3 represents a linear or branched alkylene group having 1 to 5 carbon atoms, R4 represents hydrogen atom or an alkyl group having 1 to 5 carbon atoms unsubstituted or substituted with carboxyl group (xe2x80x94COOH), carbamoyl group (xe2x80x94CONH2), hydroxyl group (xe2x80x94OH), phenyl group (xe2x80x94C6H5), hydroxyphenyl group (xe2x80x94C6H4OH), ureido group (xe2x80x94NHCONH2), methylthio group (SCH3) or 4-imidazolyl group: 
R2 and R4 form a heterocyclic group unsubstituted or substituted with hydroxyl group or oxo group in combination with Nxe2x80x94(R3)bxe2x80x94C and b represents 0 or 1.
Examples of the isothiazolone compound represented by general formula [1] include 2-methyl-4-isothiazoline-3-one, 2-ethyl-4-isothiazoline-3-one, 2-octyl-4-isothiazoline-3-one, 5-chloro-2-methyl-4-isothiazoline-3-one, 5-chloro-2-octyl-4-isothiazoline-3-one, 4,5-dichloro-2-methyl-4-isothiazoline-3-one, 4,5-dichloro-2-octyl-4-isothiazoline-3-one and 1,2-benzoisothiazoline-3-one. Examples of the isothiazolone compound represented by general formula [2] include complex compounds of the isothiazolone compounds represented by general formula [1] with magnesium chloride, magnesium nitrate, copper chloride, copper nitrate and calcium chloride.
Examples of the aminocarboxylic acid represented by general formula [3] include glycine, alanine, xcex2-alanine, valine, leucine, isoleucine, serine, threonine, asparagic acid, glutamic acid, asparagine, glutamine, sarcosine, citrulline, methionine, xcex1-aminobutyric acid, xcex2-aminobutyric acid, xcex3-aminobutyric acid, xcex5-aminocaproic acid, phenylalanine, tyrosine, histidine, proline, 4-hydroxyproline, 2-pyrrolidone-5-carboxylic acid and iminodiacetic acid.
As the compound having a structure in which the aminocarboxylic acid represented by general formula [3] is bonded through a peptide bond, compounds having a structure in which the aminocarboxylic acids represented by general formula [3] of one or more types are bonded to each other through a peptide bond are preferable. Examples of such compounds include glycylglycine, glycylglycylglycine, glycylglycyl-glycylglycine, glycylalanine, glycylasparagine, glycylleucine, glycylisoleucine, glycylphenylalanine, glycylproline, glycylsarcosine, glycylserine, glycylthreonine, glycylvaline, glycylglutamine, alanylalanine, alanylasparagine, alanylglutamine, alanylglycine, alanylphenylalanine, alanyltyrosine, xcex2-alanylhistidine, polyasparagic acid and polyglutamic acid.
Examples of the N-acetyl compound of the aminocarboxylic acid represented by general formula [3] include N-acetylglycine, N-acetylalanine, N-acetyl-L-asparagic acid, N-acetyl-L-glutamic acid and N-acetyltyrosine.
Examples of the amide of the aminocarboxylic acid represented by general formula [3] include glycineamide.
Examples of the metal salt of the compound represented by general formula [3] and the derivatives thereof include lithium salts, sodium salts, potassium salts, calcium salts and magnesium salts.
The aminocarboxylic acids represented by general formula [3] occasionally include DL-compounds, L-compounds and D-compounds. Any of DL compounds, L-compounds and D-compounds can be used in the present invention.
In the composition of the present invention, glycine and sodium glutamate are preferably used as the aminocarboxylic acid represented by general formula [3] and the derivative thereof. Glycine and sodium glutamate have advantages in that the antimicrobial composition can be prepared rapidly since these compounds have great rates of dissolution, that the amounts by weight of these compounds are smaller when these compounds are used in a prescribed amount by mol relative to an amount by mol of the isothiazolone compound represented by general formula [1] or general formula [2] since these compounds have smaller molecular weights and that these compounds are readily available since these compounds are industrially produced in large scales.
In the composition of the present invention, the concentration of the isothiazolone compound represented by general formula [1] or general formula [2] is not particularly limited. It is preferable that the concentration is 0.1 to 10% by weight and more preferably 0.5 to 8% by weight. When the concentration of the isothiazolone compound represented by general formula [1] or general formula [2] is less than 0.1% by weight, the volume of the antimicrobial composition as a commercial product increases and there is the possibility that the product is economically disadvantageous in transportation and storage. When the concentration of the isothiazolone compound represented by general formula [1] or general formula [2] exceeds 10% by weight, there is the possibility that stability of the antimicrobial composition is adversely affected.
In the present invention, the concentration of the aminocarboxylic acid represented by general formula [3] or the derivative thereof is not particularly limited. It is preferable that the aminocarboxylic acid or the derivative thereof is used in an amount by mol 0.1 to 50 times and more preferably 1 to 10 times the amount by mol of the isothiazolone compound represented by general formula [1] or general formula [2]. When the amount of the aminocarboxylic acid represented by general formula [3] or the derivative thereof is less than the amount by mol 0.1 times the amount by mol of the isothiazolone compound, there is the possibility that stability of the antimicrobial composition is insufficient and decomposition of the isothiazolone compound tends to take place and that irritation of skin is enhanced. It is generally sufficient that the amount by mol of the aminocarboxylic acid represented by general formula [3] or the derivative thereof is 50 times the amount by mol of the isothiazolone compound or less. Stability of the antimicrobial composition or the effect of reducing irritation of skin caused by the isothiazolone compound is not improved any more even when the aminocarboxylic acid represented by general formula [3] or the derivative thereof is used in an amount by mol exceeding 50 times the amount by mol of the isothiazolone compound. When the derivative of the aminocarboxylic acid represented by general formula [3] is a polyamino acid, it is preferable that the concentration of the derivative in the antimicrobial composition is 0.1 to 20% by weight.
The solvent used in the composition of the present invention is not particularly limited as long as the isothiazolone compound represented by general formula [1] or general formula [2] and the aminocarboxylic acid represented by general formula [3] or the derivative thereof are dissolved in the solvent. Because the composition is often used in an aqueous system, water or a hydrophilic organic solvent is preferable as the solvent. Examples of the hydrophilic organic solvent include amides such as dimethylformamide; glycols such as ethylene glycol, propylene glycol, diethylene glycol and dipropylene glycol; glycol esters such as methylcellosolve, phenylcellosolve, diethylene glycol monomethyl ether and dipropylene glycol monomethyl ether; alcohols having 8 or less carbon atoms; and esters such as methyl acetate, ethyl acetate, 3-methoxybutyl acetate, 2-ethoxyethyl acetate, 2-ethoxypropyl acetate and propylene carbonate. It is preferable that pH of the antimicrobial composition of the present invention is 7 or less. It is more preferable that pH of the composition is 2 to 5 to improve stability of the isothiazolone compound.
The antimicrobial composition of the present invention may further comprise corrosion inhibitors, scale inhibitors, antimicrobial agents other than the isothiazolone compounds, defoaming agents, surfactants and algicides where necessary.
Examples of the corrosion inhibitor include tolyl triazole, benzotriazole, methylbenzotriazole, molybdic acid, tungstic acid, silicic acid, nitrous acid, 2-phosphonobutane-1,2,4-tricarboxylic acid, hydroxy-ethylidenediphosphonic acid, hexametaphosphoric acid, tripolyphosphoric acid, orthophosphoric acid, salts of these compounds, zinc chloride, zinc chloride hydrochloride, zinc sulfate, zinc ligninsulfonate and hydrazine.
Examples of the scale inhibitor include polyacrylic acid, copolymers of acrylic acid and 2-hydroxyethyl methacrylate, copolymers of acrylic acid, 2-hydroxyethyl methacrylate and methyl acrylate, copolymers of acrylic acid and allyl glycidyl ether or a derivative thereof, copolymers of acrylic acid and 2-hydroxy-3-allyloxy-1-propanesulfonic acid, copolymers of acrylic acid and isoprenesulfonic acid, copolymers of acrylic acid and vinylsulfonic acid, copolymers of acrylic acid and allylsulfonic acid, polymaleic acid, copolymers of maleic acid or maleic anhydride and isobutylene, copolymers of maleic acid or maleic anhydride and styrenesulfonic acid, copolymers of maleic acid or maleic anhydride and acrylic acid, copolymers of maleic acid or maleic anhydride and 2-acrylamido-2-methylpropanesulfonic acid, copolymers of maleic acid or maleic anhydride and pentenoic acid, copolymers of maleic acid or maleic anhydride and a fluorescent substance such as 5-allylbenzosuberenol substituted with allyl group, polyacrylamide, polyitaconic acid and salts of these compounds.
Examples of the antimicrobial agent other than the isothiazolone compounds include halogenated aliphatic nitro compounds such as 2-bromo-2-nitro-1,3-propanediol and 2,2-dibromo-2-nitroethanol; esters of these compounds; dibromonitrilopropionamide; alkylene bisthiocyanates such as methylenebisthiocyanate; 1,4-bisbromoacetoxy-2-butene; hexabromo-dimethylsulfone; isophthalonitrile compounds such as 5-chloro-2,4,6-trifluoroisophthalonitrile and tetrachloroisophthalonitrile; dimethyl dithiocarbamate; 4,5-dichloro-1,2-dithiol-3-one; 3,3,4,4-tetrachloroteterahydrothiophene-1,1-dioxide; triiodoallyl alcohol; bromonitrostyrene; aldehyde compounds such as glutaraldehyde, phthalaldehyde, isophthalaldehyde and terephthalaldehyde; dichloro-glyoxime; benzaldoxime compounds such as xcex1-chlorobenzaldoxime acetate and xcex1-chlorobenzaldoxime; and 5,5-dimethylhidantoin.
Examples of the defoaming agent include silicone and non-silicone defoaming agents. Examples of the surfactant include anionic, cationic, nonionic and amphoteric surfactants. Examples of the algicide include triazine compounds such as ametryne.
The embodiments of the composition of the present invention include antimicrobial compositions containing 0.1 to 10% by weight of the isothiazolone compound represented by general formula [1] or general formula [2], 0.1 to 20% by weight of the aminocarboxylic acid represented by general formula [3] or the derivative thereof, 0 to 50% by weight of corrosion inhibitors, 0 to 50% by weight of scale inhibitors, 0 to 30% by weight of other antimicrobial agents, 0 to 10% by weight of defoaming agents, 0 to 10% by weight of surfactants, 0 to 10% by weight of algicides and 30 to 99% by weight of water or a hydrophilic organic solvent.
The antimicrobial composition of the present invention can be used in a concentration suitably selected in accordance with the subject and the object of the application. For example, when the composition is used for prevention of slime in a paper and pulp manufacturing system or in a cooling water system, it is preferable that the concentration of the isothiazolone compound is 0.1 to 25 g/m3. When the composition is used for prevention of putrefaction of an emulsion of a synthetic resin, a starch paste, a starch slurry, a coating material or an oil for metal working, it is preferable that the concentration of the isothiazolone compound is 1 to 5,000 g/m3.
The antimicrobial composition of the present invention contains the isothiazolone compound and the aminocarboxylic acid or the derivative thereof, shows excellent stability under heating and for a long time, does not cause decomposition of the isothiazolone compound for a long time, exhibits the excellent antimicrobial effect derived from the isothiazolone compound and can be easily handled due to decreased irritation of skin caused by the isothiazolone compound.